Imaging systems for use with gamma and X-radiation have been built with a scintillation camera and a mask as disclosed in the U.S. Pat. No. 3,748,470 which issued in the name of H. H. Barrett on July 24, 1973, and with a plurality of masks from a common family of masks such as Fresnel masks as is disclosed in the United States Pat. No. 3,961,191 which issued in the names of W. W. Stoner et al on June 1, 1976. While such systems are capable of producing images of a subject, it is desired to produce images of still higher quality. However, the coded images or shadowgrams produced on the scintillation camera result from a non-diffracting situation in which the radiation is not diffracted by the mask. In contrast to a lens, or Fresnel plate utilized as a lens, as are customarily employed in optical situations wherein diffracted radiation can be described mathematically by complex numbers having both amplitude and phase data, the non-diffracted radiation provides only amplitude data with an attendant increase in the difficulty of image reconstruction.